Macbook Pro keyboard backlit lights up not appropriately
I got a problem with the keyboard backlit of my 15 MBP. It worked fine before: being off in the daytime and in the evening with the lamp on in my room, and lighted up when I turned off my lamp. But now, it always lights up even the lamp is on. I'm sure there is nothing covered the sensor under the speakers. It doesn't light up in the daytime. Seems the threshold of lighting up the backlit has been changed. I got the problem once before and the problem was disappeared after I re-installed Tiger, I don't know why. Now I suffer this again after I upgraded my OS to Leopard. The keyboard backlit works good in Windows installed with Boot Camp, so I think the hardware is fine and there must be some configuration changed by some way.
Does anyone know how I can solve this problem, or if there is any software can change the threshold of the backlit, or should I reset something?
Thank you very much in advance.
Macbook Pro, Mac OS X (10.5)